Microelectronics continues to impact society in a multitude of ways every day. The semiconductor revolution is the engine that drives cell phones, the internet, flat-panel televisions, flash memory chips, global positioning system devices, solar cells, etc. Microelectronics has had a profound impact on the fields of biomedicine, transportation, communications, entertainment, defense, environmental monitoring, and homeland security.
For more than three decades optical lithography has been the recipe for success to meet the semiconductor industry's steady decrease in device size as described by Moore's law. In 1965, Gordon Moore, the co-founder of Intel, predicted that the number of transistors in a commercial integrated circuit would double every two years. Up until now, this prediction has accurately stood the test of time. However, since the second decade of the twenty first century, there has been serious doubt that conventional optical lithography can continue to provide the needed decreasing sizes. Efforts to decrease the wavelength of the source (e.g. from 192 nm to 157 nm) have not been successful. Increasing the surrounding refractive index in immersion lithography (e.g. from 1.44 to 1.65) remains in research and development. New approaches are needed. Techniques being considered include 1) self-assembly approaches; 2) construction-based approaches including immersion lithography, double patterning, double exposure, two-photon lithography, printing, direct writing, source mask optimization, and micromanipulation; and 3) interference lithography.
Modern integrated circuits have very regular layouts with an underlying grid pattern that defines the smallest feature size in the integrated circuit. Multi-beam interference lithography (MBIL) can be used to define this underlying grid. MBIL immediately has the advantages of 1) simple optics, 2) large working distances, 3) high-speed processing, 4) low cost, and 5) extendable to higher resolutions. As such, MBIL could be a cornerstone for future optical lithography systems. The flexibility of interference lithography to produce maskless high-spatial-frequency periodic patterning, combined with other lithographic techniques (e.g. projection lithography, e-beam lithography, self-assembly), should play a key role in sustaining the demands of the microelectronics industry to reduce feature size with simple, inexpensive, large-area periodic nanoscale patterning.
Several other technologies, such as photonic crystal technology, metamaterials, biomedical structures, subwavelength structures, and optical traps can be developed or improved by new advances in MBIL technologies. For example, photonic crystal technology has many important possible commercial applications. The technology potentially offers lossless control of light propagation at a size scale near the order of the wavelength of light. This technology has the potential to produce the first truly dense integrated photonic circuits and systems (DIPCS). Individual components that are being developed include resonators, antennas, sensors, multiplexers, filters, couplers, and switches. The integration of these components would produce DIPCS that would perform functions such as image acquisition, target recognition, image processing, optical interconnections, analog-to-digital conversion, and sensing. Further, the resulting DIPCS would be very compact in size and highly field-portable. Applications using light at telecommunications wavelengths require structures to be fabricated with nano-sized dimensions. Despite the advantages and benefits of using such a technology in commercial devices, the practical commercial development of PC structures has been very slow.